A wireless communication system has been widely developed to provide various kinds of communication services such as voice and data. Generally, the wireless communication system is a multiple access system that can support communication with multiple users by sharing available system resources (bandwidth, transmission power, etc.). Examples of the multiple access system include a code division multiple access (CDMA) system, a frequency division multiple access (FDMA) system, a time division multiple access (TDMA) system, an orthogonal frequency division multiple access (OFDMA) system, a single carrier frequency division multiple access (SC-FDMA) system, and a multi carrier-frequency division multiple access (MC-FDMA) system. In the wireless communication system, a user equipment may receive information from a base station through a downlink, and may transmit information to the base station through an uplink. Examples of information transmitted from or received in the user equipment include data and various kinds of control information. Various physical channels exist depending on a type and usage of the information transmitted from or received in the user equipment.
In the wireless communication system, since a channel between a transmitter and a receiver is not fixed, it is required to frequently measure a channel between a transmitting antenna and a receiving antenna. If the transmitter and the receiver transmit and receive a signal mutually prescribed to and from each other to measure a channel, a phase shifted value and a decreasing amount of amplitude caused by the channel may be identified. And, the identified information may be fed back to a transmitting side. Alternatively, data information which is not prescribed may reliably be detected and decoded using the identified information. The signal prescribed between the transmitter and the receiver may be referred to as a reference signal, a pilot signal or a sounding reference signal.
A 3rd generation partnership project long term evolution (3GPP LTE) communication system which is an example of a mobile communication system to which the present invention can be applied will be described in brief.
FIG. 1 is a diagram illustrating a network structure of an Evolved Universal Mobile Telecommunications System (E-UMTS) which is an example of a mobile communication system. The E-UMTS is an evolved version of the conventional UMTS, and its basic standardization is in progress under the 3rd Generation Partnership Project (3GPP). The E-UMTS may generally be referred to as a Long Term Evolution (LTE) system. For details of the technical specifications of the UMTS and E-UMTS, refer to Release 7 and Release 8 of “3rd Generation Partnership Project; Technical Specification Group Radio Access Network”.
Referring to FIG. 1, the E-UMTS includes a User Equipment (UE) 120, base stations (eNode B and eNB) 110a and 110b, and an Access Gateway (AG) which is located at an end of a network (E-UTRAN) and connected to an external network. Generally, the base stations may simultaneously transmit multiple data streams for a broadcast service, a multicast service and/or a unicast service.
One or more cells may exist for one base station. One cell is set to one of bandwidths of 1.25, 2.5, 5, 10, and 20 MHz to provide a downlink or uplink transport service to several user equipments. Different cells may be set to provide different bandwidths. Also, one base station controls data transmission and reception for a plurality of user equipments. The base station transmits downlink (DL) scheduling information of downlink data to the corresponding user equipment to notify the user equipment of time and frequency domains to which data will be transmitted and information related to encoding, data size, hybrid automatic repeat and request (HARQ). Also, the base station transmits uplink (UL) scheduling information of uplink data to the corresponding user equipment to notify the user equipment of time and frequency domains that can be used by the corresponding user equipment, and information related to encoding, data size, and HARQ. An interface for transmitting user traffic or control traffic may be used between the base stations. A Core Network (CN) may include the AG and a network node or the like for user registration of the user equipment UE. The AG manages mobility of the user equipment UE on a Tracking Area (TA) basis, wherein one TA includes a plurality of cells.
Although the wireless communication technology developed based on WCDMA has been evolved into LTE, request and expectation of users and providers have continued to increase. Also, since another wireless access technology is being continuously developed, new evolution of the wireless communication technology will be required for competitiveness in the future. In this respect, reduction of cost per bit, increase of available service, use of adaptable frequency band, simple structure, open type interface, proper power consumption of the user equipment, etc. are required.
Recently, standardization of advanced technology of LTE is in progress under the 3rd Generation Partnership Project (3GPP). This technology will be referred to as “LTE-Advanced” or “LTE-A.” One of important differences between the LTE system and the LTE-A system is difference in system bandwidth. The LTE-A system aims to support a wideband of maximum 100 MHz. To this end, the LTE-A system uses carrier aggregation or bandwidth aggregation that achieves a wideband using a plurality of frequency blocks. For wider frequency bandwidth, carrier aggregation aims to use a plurality of frequency blocks as one great logical frequency band. A bandwidth of each frequency block may be defined based on a bandwidth of a system block used in the LTE system. Each frequency block is transmitted using a component carrier.